Layered Bi4BaxV2–xO11–(3x/2)–δ perovskite oxide as solid electrolyte for intermediate temperature solid oxide fuel cells

A continuous series of Bi4BaxV2–xO11–(3x/2)–δ solid solutions are prepared by conventional solid state reactions. The polymorphism and electrical properties of these samples are studied by FT-IR spectroscopy, X-ray diffraction, differential thermal analysis (DTA) and AC impedance. The solid solutions with composition 0.07≤x≤0.13 are isostructural with the monoclinic phase α-Bi4V2O11. However, orthorhombic β-phase is observed for x=0.17 and tetragonal γ-phase is stabilized for x≤0.30. X-ray and DTA results reveal the occurrence of α↔γ transition for x≤0.13, β↔γ transition for x=0.17 and γ′→γ transition for x≥0.20. AC impedance plots at 280 °C for all compositions show greater contribution of grain to ionic conductivity than grain boundary. The highest ionic conductivity, σ300 °C=4.456×10–5 S cm–1 is observed for x=0.17. The ionic conductivity of the substituted compounds is higher than the parent α-Bi4V2O11, due to the increased oxygen ion vacancies generated as a result of barium doping.